In recent years, radioactive materials have spread across wide areas due to accidents of nuclear power plants, and not only have areas around the power plants been affected but also areas with a high level of radiation dose have been generated as hot spots. Thus, the influence of radiation exposure on residents in the neighboring areas is concerned.
From such circumstances, it is strongly demanded that not only the radiation doses of the neighboring areas or work areas to be decontaminated be measured and monitored, but also a radiation exposure sensor be provided on the human body to measure the level of radiation exposure of the human body through his/her whole-day activities for a long term so that the measured data can be used to decontaminate the neighboring areas or avoid radiation exposure of individuals.
As the simplest means for measuring the radiation exposure dose, there is known a film badge dosimeter that uses a chemical change of a substance that occurs upon incidence of radiation on the substance. Further, an electronic radiation dosimeter has also been used that counts pulse signals of radiation using a Geiger-Mueller counter and a diode, which is a semiconductor element, or using a scintillator and a photodiode, and displays the radiation dose by multiplying the count number by a scale factor.
The film badge dosimeter can only measure the cumulative value of the radiation exposure dose from the time the dosimeter is worn, and thus cannot measure how much and when a measured object was exposed to radiation or cannot accurately identify a place with a high radiation dose.
Patent Literature 1 and Patent Literature 2 below each propose a wrist-mount or clip-mount portable radiation dosimeter that includes a radiation detection unit having silicon semiconductor elements, a microcomputer, a display unit such as a LCD, and the like.